1. Field of the Invention
This invention relates to a method and an apparatus for lighting a solder bump on a BGA (Ball Grid Array) board, and more particularly to a method and an apparatus for lighting and inspecting a solder bump.
2. Description of the Related Art
A circuit board wherein spherical solder bumps are mounted on the surfaces of connection pads in order to mount a circuit chip on the surface of the circuit board is available at present and normally called BGA board. A circuit board of the type described, however, sometimes suffers from peeling off of a solder bump during working, and this gives rise to failure in connection of a circuit chip mounted on the surface of the circuit board.
In order to solve the problem described, another BGA board has been proposed wherein a reinforcing resin is applied to a solder bump after the solder bump is attached to the surface of the board so that a lower half of the solder bump is held to the board by the reinforcing resin. The BGA board prevents peeling off of the solder bump from the circuit board during working because the connection between the solder bump and the circuit board is reinforced by the reinforcing resin.
However, since the reinforcing resin is an insulator, if it is applied up to an upper portion of a solder bump, then this causes failure in connection of a circuit chip mounted on the surface of the circuit board. Therefore, it is necessary to inspect a condition of the reinforcing resin applied to a solder bump, and an effective technique for inspecting has not been developed.
A possible solution, for example, would be to use visual inspection to inspect the condition of a reinforcing resin applied to a solder bump. In recent years, however, solder bumps are smaller in size and mounted at a higher density, and it is not practical to inspect a large number of solder bumps of BGA boards produced in a mass by visual inspection.
For example, Japanese Patent Laid-Open Publication No. 311020/1997 and Japanese Patent Laid-Open Publication No. 147467/1996 disclose a method of and an apparatus for inspecting the outside shape of a solder bump. Although the method and apparatus allows inspection of an outside shape of a solder bump, it does not allow inspection of the condition of a reinforcing resin applied to a solder bump.
It is an object of the present invention to provide a bump lighting method and apparatus which lights a solder bump so that the condition of a reinforcing resin which has been applied can be inspected well.
It is another object of the present invention to provide a bump image capturing method and apparatus which captures an image of a solder bump so that the condition of a reinforcing resin which has been applied can be inspected well.
It is a further object of the present invention to provide an image processing method and apparatus which determines from image data of a solder bump whether the condition of an applied reinforcing resin is good or bad.
It is still a further object of the present invention to provide a bump inspecting method and apparatus which inspects the condition of a reinforcing resin applied to a solder bump well.
It is yet a further object of the present invention to provide an information storage medium to store a program for enabling a computer to execute a determination from image data of a solder bump whether the condition of an applied reinforcing resin is good or bad is stored as software.
The bump lighting apparatus according to the present invention lights a spherical solder bump having a reinforcing resin applied to the lower half mounted on the surface of a circuit board and comprises a board holding mechanism for holding the circuit board at a predetermined position, and an irradiating mechanism for irradiating rays of light upon the outer periphery of a solder bump from all circumferential directions such that the rays of light may intersect at a predetermined angle with the surface of the circuit board held by the board holding mechanism.
Accordingly, in the bump lighting apparatus, the rays of light which intersect at the predetermined angle with the surface of the circuit board held at the predetermined position by the board holding mechanism are irradiated from all circumferential directions upon the outer periphery of the solder bump by the irradiating mechanism. Since the position of the boundary between the upper half of the spherical solder bump and the reinforcing resin can be lighted substantially uniformly, the bump lighting apparatus can light the solder bump and the reinforcing resin well for distinguishing them from each other.
In the bump lighting apparatus, the irradiating mechanism may include a plurality of light-emitting devices for individually emitting rays of light, and a light source holding mechanism for holding the light-emitting devices in an inwardly radially directed condition so that the rays of light emitted from the light-emitting devices may be concentrated at a point.
In this case, the plurality of light-emitting devices are disposed in an inwardly radially directed condition by the light source holding mechanism, and the rays of light individually emitted from the light-emitting devices are concentrated upon the one point. Consequently, the rays of light are irradiated upon the outer periphery of the solder bump from all circumferential directions. The irradiating mechanism which irradiates the rays of light in this manner can be implemented with a simple structure of a small number of parts.
In the bump lighting apparatus, the irradiating mechanism may include a plurality of light-emitting devices for individually emitting rays of light, a light source holding mechanism for holding the light-emitting devices in a circular fashion, and a light diverting mechanism for diverting the rays of light emitted from the light-emitting devices arranged on the light source holding mechanism so that the rays of light may be concentrated at a point.
In this case, the plurality of light-emitting devices are disposed in a circular fashion by the light source holding mechanism, and the rays of light individually emitted from the light-emitting devices are diverted in predetermined directions and concentrated at one point by the light converting mechanism. Consequently, the rays of light are irradiated upon the outer periphery of the solder bump from all circumferential directions by the irradiating mechanism. The irradiating mechanism which irradiates the rays of light in this manner can be formed in a structure which allows easy disposition of the light-emitting devices.
The bump lighting apparatus may further comprise a light converting member for converting the rays of light to be irradiated upon the solder bump into polarized light. In this case, since the rays of light to be irradiated upon the solder bump are converted into polarized light by the light converting member, reflected light from a solder bump with a mirror surface can be prevented from having an extremely high intensity.
In the bump lighting apparatus, the light-emitting devices may emit rays of light of a color substantially complementary to the coloring of the reinforcing resin. In this case, since the rays of light to be irradiated upon the solder bump from the light-emitting devices has a substantially complementary color to the coloring of the reinforcing resin, the rays of light are reflected well from the solder bump whose surface is formed as a mirror surface, and the reinforcing resin absorbs most of the rays of light irradiated thereupon. Accordingly, the bump lighting apparatus can light a solder bump and the reinforcing resin for distinguishing them well from each other.
The bump image capturing apparatus according to the present invention capture an image of a spherical solder bump having a reinforcing resin applied to the lower half, mounted on the surface of a circuit board and comprises a bump lighting apparatus for holding the circuit board at a predetermined position to light the solder bump, an image capture apparatus for capturing an image of reflected light from the solder bump lighted by the bump lighting apparatus from a direction perpendicular to the surface of the circuit board, and an intensity adjusting mechanism for lowering the intensity of the light reflected from the central portion of a solder bump within the image capture range of the image capture apparatus.
Consequently, according to the method for capturing a bump image by the capturing apparatus of the present invention, the circuit board is held at a predetermined position and the solder bump is lighted by the bump lighting apparatus, and the image of reflected light from the lighted solder bump is captured from the direction perpendicular to the surface of the circuit board image capture apparatus. However, since the intensity of the reflected light from the central portion of a solder bump in the image capture range of the image capture apparatus is lowered by the intensity adjusting mechanism, the intensity of the rays of light reflected from the top portion of the solder bump whose surface is formed as a mirror surface is lowered to a level suitably capturing with which the rays of light. Consequently, an image of a solder bump likely to reflect light intensity from the top portion can be captured well without suffering from exposure to excessive light.
In the bump image capturing apparatus, the intensity adjusting mechanism may include an optical filter having a transmittivity which with a concentrical variation which decrease toward the center, and a filter disposing mechanism for disposing the optical filter in the gap between the image capture apparatus and the solder bump.
In this case, since the optical filter is disposed in the gap between the image capture apparatus and the solder bump by the filter disposing mechanism and the optical filter has a transmittivity which toward the center decreases concentrically, the intensity of reflected light from the central portion of a solder bump in the image capture range of the image capture apparatus can be lowered with certainty with a simple structure by the intensity adjusting mechanism.
In the bump image capturing apparatus, the intensity adjusting mechanism may adjust the intensity of the light reflected from the solder bump to be imaged to the dynamic range of the image capture apparatus. In this case, since the intensity of the light reflected from the solder bump to be imaged is adjusted to the dynamic range of the image capture apparatus by the intensity adjusting mechanism, the image capture apparatus can capture an image of the solder bump in a condition of good light exposure. Another bump image capturing apparatus is applied to capture an image of a spherical solder bump having a reinforcing resin applied to the lower half, mounted on the surface of a circuit board and comprises a bump lighting apparatus for holding the circuit board at a predetermined position to light the solder bump, an image capture apparatus for capturing an image of reflected light from the solder bump lighted by the bump lighting apparatus from a direction perpendicular to the surface of the circuit board, a first light converting member for converting the light upon the solder bump irradiated by the bump lighting apparatus into polarized light, and a second light converting member for converting the light reflected from the solder bump and to be imaged by the image capture apparatus into polarized light.
Accordingly, in the bump image capturing apparatus according to the present invention, the circuit board is held at a predetermined position and the solder bump is lighted by the bump lighting apparatus, and an image of reflected light from the lighted solder bump is captured from a direction perpendicular to the surface of the circuit board by the image capture apparatus. However, the rays of light to be irradiated upon the solder bump from the bump lighting apparatus are converted into polarized light by the first light converting member, and the rays of light reflected from the solder bump and to be imaged by the image capture apparatus are converted into polarized light by the second light converting member. Consequently, the intensity of the rays of light reflected from the top portion of the solder bump is lowered to a level suitably capturing with which the rays of light, and an image of a solder bump likely to reflect light intensity from the top portion can be captured well without suffering from exposure to excessive light.
In the bump image capturing apparatus, the bump lighting apparatus may be the bump lighting apparatus according to the present invention described above.
In this case, the position of the boundary between the spherical solder bump and the reinforcing resin is lighted substantially uniformly from all circumferential directions by the bump lighting apparatus according to the present invention, and the image of the solder bump thus lighted is captured by the bump image capturing with the intensity of reflected light lowered at least at the top portion of the solder bump. Accordingly, the bump image capturing apparatus can capture an image of the solder bump and the reinforcing resin under condition in which they can be distinguished well from each other.
The image processing apparatus according to the present invention is applied to process image data of a spherical solder bump having a reinforcing resin applied to the lower half, mounted on the surface of a circuit board and comprises image converting means for converting the multilevel image data in binary form, object extracting means for extracting an object from the binary image data by the image converting means corresponding to the portion of a solder bump exposed above the reinforcing resin, and quality determining means for determining whether the object extracted by the object extracting means is good or bad.
Accordingly, in the image processing apparatus according to the present invention, the multilevel image data are converted in binary form by the image converting means, and an object corresponding to the portion of a solder bump exposed above the reinforcing resin is extracted from the binary image data by the object extracting means, and the quality of extracted object is determined by the quality determining means. Consequently, the quality of the state of the reinforcing resin applied to the solder bump can be determined. Because of no need to inspect a very large number of very small solder bumps by visual observation, the yield of circuit boards can be increased.
The image processing apparatus may further comprise range limiting means for limiting the processing range of image data to a circular shape corresponding to the outside shape of a solder bump. In this case, limitation of the processing range of the image data to a circular shape corresponding to the outside shape of the solder bump by the range limiting means, enables image data only of the portion of a solder bump necessary for determining the state of the reinforcing resin applied to the solder bump to be processed, and various image processes to be completed rapidly.
In the image processing apparatus, the image converting means may include average detecting means for detecting an average brightness of the image data in the circumferentially inward portion of the circle limited by the range limiting means, and threshold value calculating means for adding a predetermined offset value to the average brightness detected by the average detecting means to calculate a threshold value for conversion in binary form.
In this case, an average brightness of the image data in the circumferentially inward portion of the circle limited by the range limiting means is detected by the average detecting means, and the predetermined offset value is added to the average brightness by the threshold value calculating means to calculate a threshold value for conversion in binary form. Since the image converting means converts the multilevel image data in binary form with the threshold value, the image data can be converted in binary form so that the solder bump and the reinforcing resin are distinguished well from each other.
The image processing apparatus may be constructed such that it further comprises process controlling means for controlling at least the processing operation of the quality determining means, and that the object extracting means includes means for successively scanning the image data of one solder bump to successively extract a plurality of objects while the quality determining means includes means for successively inspecting the plurality of objects corresponding to the one solder bump, and the process controlling means includes means for completing the processing of the quality determining means at the point in time when one good object is detected from among the plurality of objects.
In this case, the image data of one solder bump are successively scanned by the object extracting means to successively extract a plurality of objects, and the plurality of objects corresponding to the one solder bump are successively inspected by the quality determining means. However, at the point in time when one good object is detected from among the plurality of objects, the processing of the quality determining means for the remaining objects is omitted by the process controlling means. Consequently, since the processing for the plurality of objects is limited to minimum necessary processing and unnecessary processing is not executed, the processing can be completed rapidly.
In the image processing apparatus, the object extracting means may extract one object from the image data at a central portion. In this case, since one object is extracted from the image data at a central portion by the object extracting means, the object of the portion of a solder bump exposed above the reinforcing resin can be extracted at one time, and this processing can be completed rapidly.
In the image processing apparatus, the quality determining means may include area detecting means for detecting the area of an object extracted by the object extracting means, and area comparing means for comparing the area detected by the area detecting means with a predetermined tolerance.
In this case, the area of the object extracted by the object extracting means is detected by the area detecting means, and the area is compared with the predetermined tolerance by the area comparing means. Consequently, since whether the area of an upper portion of the solder bump exposed above the reinforcing resin is suitable or not is determined by the quality determining means, the quality of the state of the reinforcing resin applied to the solder bump can be determined simply.
In the image processing apparatus, the quality determining means may include ratio detecting means for detecting the aspect ratio of the object extracted by the object extracting means, and ratio comparing means for comparing the aspect ratio detected by the ratio detecting means with a predetermined tolerance.
In this case, the aspect ratio of the object extracted by the object extracting means is detected by the ratio detecting means, and the aspect ratio is compared with the predetermined tolerance by the ratio comparing means. Consequently, since whether the shape of an upper portion of the solder bump exposed above the reinforcing resin is suitable or not is determined by the quality determining means, the quality of the state of the reinforcing resin applied to the solder bump can be determined simply.
In the image processing apparatus, the ratio detecting means may detect the major axis of the object extracted by the object extracting means and use the detected major axis of the object as a vertical axis.
In this case, the major axis of the object extracted by the object extracting means is detected by the ratio detecting means as a vertical axis, and the aspect ratio of the object is detected with respect to the vertical axis. Since the aspect ratio of the object can be detected as a ratio between the major axis and the minor axis, a deformed object due to noise can be prevented from being recognized in error as a substantially circular object of the exposed portion of a solder bump.
The bump inspecting apparatus according to the present invention comprises the bump image capturing apparatus and the image processing apparatus.
Accordingly, in the bump inspecting apparatus according to the present invention, the position of the boundary between the spherical solder bump and the reinforcing resin is lighted substantially uniformly from all circumferential directions by the bump lighting apparatus of the present invention, and an image of a solder bump thus lighted is captured by the bump image capturing apparatus according to the present invention under condition in which the intensity of reflected light lowered at least at the top portion of the solder bump. Since the quality of the state of the reinforcing resin applied to the solder bump is determined based on the image data captured in this manner by the image processing apparatus according to the present invention, the state of the reinforcing resin applied to the solder bump can be inspected well.
The bump inspecting apparatus may be constructed such that the circuit board has a plurality of solder bumps disposed on the surface thereof and that it further comprises a relative moving mechanism for moving the board holding mechanism relative to the irradiating mechanism and the image capture apparatus, and a central controller for integrally controlling the relative moving mechanism, the bump lighting apparatus, the bump image capturing apparatus and the image processing apparatus to successively light and capture an image of the solder bumps on the surface of the one circuit board to inspect the solder bumps.
In this case, the relative moving mechanism, bump lighting apparatus, bump image capturing apparatus and image processing apparatus are integrally controlled by the central controller so that the solder bumps on the surface of the one circuit board which is relatively moved by the relative moving mechanism are successively lighted by the bump lighting apparatus and captured by the bump image capturing apparatus and then inspected by the image processing apparatus. Since the state of the reinforcing resin applied is successively inspected for a large number of solder bumps disposed on the surface of the one circuit board, a large number of solder bumps of the one circuit board can be inspected automatically.
It is to be noted that the various means in the present embodiment are required only to be formed so as to implement the functions assigned thereto, and may be, for example, hardware for exclusive use, a computer to which suitable functions are provided by a program, functions implemented in the inside of a computer by an appropriate program, or a suitable combination of these.
An information storage medium according to the present invention stores a program therein for enabling a computer to execute a process of inputting image data of a spherical solder bump having a reinforcing resin applied to the lower half, mounted on the surface of a circuit board, a process of converting the inputted multilevel image data in binary form, a process of extracting the object corresponding to the portion of a solder bump exposed above the reinforcing resin from the binary image data, and a process of determining whether the extracted object is good or bad.
When the program stored in the information storage medium according to the present invention is read by a computer so that the computer may execute corresponding processes, the computer inputs image data of a spherical solder bump having a reinforcing resin applied to the lower half, mounted on the surface of a circuit board, and converts the inputted multilevel image data in binary form. Then, the computer extracts an object corresponding to the portion of a solder bump exposed above the reinforcing resin from the binary image data, and determines the quality of the extracted object. Consequently, the quality of the state of the reinforcing resin applied to the solder bump can be determined by the computer.
It is to be noted that the information recording medium in the present invention may be any medium on which a program for enabling a computer to execute various processes is stored in advance as software, and may be, for example, a ROM (Read Only Memory) or a HDD (Hard Disc Drive) fixed to an apparatus which includes a computer as a component, or a CD-ROM (Compact Disc ROM) or a FD (Floppy Disc) which is removably loaded into an apparatus which includes a computer as a component.
Further, the computer in the present invention may be any apparatus which can read a program of software and execute corresponding processing operation, and may be, for example, an apparatus which includes a CPU (Central Processing Unit) as a principal component and includes various devices such as a ROM, a RAM (Random Access Memory) and an I/F (Interface) connected to the CPU as necessary. In the present invention, to cause a computer to execute various operations corresponding to software may be to cause a computer to control operation of various devices.
The above and other objects, features and advantages according to the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples according to the present invention.